A lot of Arizonans are upset about illegal immigration, and to learn why, you can't do better than the letter from Arizona State Sen. Sylvia Allen. Widely circulated on the Internet, it provides a pungent statement of the frustrations behind the new law stiffening enforcement -- while confirming that it's the wrong remedy.

People on the border, she writes, "have pleaded for help to stop the daily invasion of humans who cross their property." The migrants damage fences, scatter trash and sometimes perish en route. "One rancher testified that 300 to 1,200 people a DAY come across his ranch," reports Allen.

The illegal entries, she believes, undermine our status as "a nation of laws." With a state budget deficit, "we do not have the money to care for any who are not here legally," she says.

Hers are not the only complaints being heard. Among others: Illegals don't pay taxes. They steal Social Security numbers to get jobs. They drive down wages by working off the books.

All no doubt true. But the legislation assumes that tougher enforcement at the border and within the state will magically banish these problems. In fact, those options have already been tried, and all they have done is make things worse.

The supporters of the law, meanwhile, overlook the obvious. There is a simple way to stop the lawless stream, protect Americans living on the border, improve adherence to law and reduce the costs of accommodating people who have no right to be here.

The solution? Stop focusing on trying to keep illegal immigrants out and start focusing on letting legal immigrants in.

Enforcement-only advocates often say they are not opposed to foreigners coming here as long as they follow the rules and obey the law. They should take a number and wait their turn, we are told, like the teeming masses of yore. It makes perfect sense until you discover that for most of those who want to come, legal admission is just about impossible.

"A peaceful, hardworking 24-year-old in Mexico or Central America who knows of a job in the United States for which no Americans are available simply has no legal means of entering the United States," writes policy analyst Daniel Griswold of the libertarian Cato Institute.

Foreigners with in-demand skills, like computer scientists, may get work visas. Close relatives of legal immigrants can also be admitted, though they often have to wait years. But if you don't fit in one of those slots -- well, how do you say "fugheddaboutit" in Spanish?

Griswold suggests a big boost in the number of temporary worker visas, which would mean Mexicans and Nicaraguans would no longer have to undertake a death-defying trek across the Sonoran Desert, or squeeze into the trunk of a smuggler's car, for the privilege of working at a sweaty, low-wage job.

They wouldn't need to swipe Social Security numbers to get counterfeit documents. They would be far more likely to work on the books and pay taxes. They would come under the cover of federal and state labor regulations, so they would no longer undercut native employees.

They would stop enriching Mexican criminal organizations that make a business of human trafficking. They would gain more of a stake in participating in and preserving our way of life.

Xenophobes might fear that expanding legal immigration would produce a big jump in the foreign-born population. That's unlikely, because in this realm, the paradoxical often prevails.

Trying to lock down the border has not stanched the flow of unauthorized newcomers from the south, but it has made the trip much more dangerous and expensive. So illegal foreigners who once came and left now come and stay.

Thirty years ago, nearly half of undocumented arrivals departed within a year. Today, only one in 14 does.

If most of the 12 million illegal immigrants were to gain authorized status, many would feel free to return to their native countries, and some would remain there. Permitting more legal immigrants, oddly, could reduce the number of total immigrants.

If there is any lesson from recent experience, it's that foreigners are going to come here one way or another. The best option is to admit far more of them through wider legal channels. The alternative is to keep Arizona's southernmost ranches as the front line of a war the immigrants don't want and we can't win.